Rain, Ice, Snow Incoming to New England this Weekend

After brief surface ridging between systems on Friday and Saturday, New England's next system will approach later Saturday and Sunday. This will be a frontal system with a primary low lifting well north of New England. A secondary low is poised to lift through northern New England, making this system an inside runner. This will lift a warm front into New England, drawing milder air into the region and preventing a widespread snowfall across a large swath of the region.

Trends over the past couple days have pointed to a weaker storm system that is quicker moving. The system will likely arrive in western New England Saturday evening. The storm will steadily spread eastward through the rest of Saturday night before peaking for most early Sunday morning. The storm now looks progressive enough that it may be largely pushing out of New England through Sunday morning. Spot showers and flurries will be possible behind the system's cold front.

Below: FV3 showing potential weather Saturday evening (1st image) and the pre-dawn hours Sunday (2nd image):

Maine, being the farthest east, will naturally hang onto the storm the longest on Sunday during the day. The storm will likely be undergoing some form of cyclogenesis as it moves east of New England. This would allow wrap-around snow to linger longer across eastern Maine. The precipitation across eastern Maine is more likely to be snow rather than a mix or rain. The secondary low's track has trended a bit farther south over the past 24 hours, which does increase the odds of a snowstorm across eastern Maine as colder air gets locked in.

Below: FV3 showing potential weather Sunday morning:

There will likely be plenty of cold air at the surface when precipitation begins to arrive early Sunday morning. This will come as the system lifts its warm front across New England, allowing warmer air to ride over the colder air at the surface. This is a prime setup for a rather messy storm across northern New England with a period of snow, sleet, freezing rain and plain rain all possible. The cold air in southern New England looks marginal at best, which is why the system will likely end up being a majority of rain with only a bit of mixing at the start.

With a warm front overrunning cold air at the surface during the overnight hours, it will likely set up a cold air damming situation. Cold air damming occurs when a low-level cold air mass basically gets trapped by the mountains. With a warm nose of air rising aloft, it can lead to a period of freezing rain with warm air across the mid-levels and cold air remaining at the lower levels.

This allows for sleet and/or freezing rain to fall instead of snow or plain rain. The issue with cold air damming is that models tend to have a "warm bias", meaning they tend to push the colder air out too fast. Cold air in these situations are often stubborn and slower to scour out than guidance often suggests.

Below: Diagram of cold air damming:

Exact precipitation types and amounts will be determined by the secondary low's strength and exact track. Not only has the track trended farther south, but the system has also trended weaker overall. Both of these favor cooler temperatures and lighter precipitation. What this may do is allow for a longer period of a wintry mix over interior northern New England. With that said, precipitation would also be generally lighter in this scenario, so this is expected to remain a rather low-impact system for most. This would be especially true for western New Hampshire and the northern half of Maine.

Given the expected setup, the most dominant wintry precipitation looks to be freezing rain rather than sleet. This will come as warm air moves into New England aloft with colder air staying at the surface initially. Given the overall setup, this will likely be a deep layer of warmer air, and with colder air at the surface getting scoured out, freezing rain is expected to win out over sleet. Freezing rain accretions of a glaze to a tenth of an inch are possible, with the highest amounts across Vermont. Probabilities for any icing outside of a very quick glaze across southern New England and near the northern New England coast are slim.

As the storm strengthens and slides southward into the eastern Gulf of Maine, colder air will likely get locked in for northern Maine. This will also allow for a period of heavier precipitation, allowing for decent snow accumulations. Again, exactly where the line between mixing occurs and mostly snow occurs across interior Maine will be determined by the system's ultimate track, which has been waffling back and forth over the past few days.

Also, on the backside of the system, colder air will wrap around and upslope snow will be likely across the higher terrain of northern New England. This would likely occur later Sunday and into Monday morning. This should help tack on some snow accumulations to areas that didn't see much at the onset Saturday night.

Below: RGEM showing potential Sunday evening:

This system will set up another chilly week next week. Winds will be elevated after the cold front passage, with gusts of 30-40mph likely later Sunday and Monday for most. High pressure is poised to build back into New England around mid-week. Winds will likely begin to pick up rather quickly behind the departure of precipitation on Sunday for many.